Optical emission spectroscopy, quadrupole mass spectrometry, and microwave phase measurements of electron density were used to study the characteristics of SiCl4 /N-2 plasmas and their resulting etch processes. The addition of N-2 to SiCl4 plasmas enhanced the etch rate of GaAs from 1000 angstrom/min in pure SiCl4 to 2300 angstrom/min in a 40:60 SiCl4: N-2 mixture (15 mTorr, - 200 V, 10 sccm). The optical emission intensities of atomic and molecular chlorine remained nearly constant with increasing N2 percentage (up to 20% N-2), but an argon actinometer exhibited a large increase in optical emission intensity with N-2 addition, indicating a shift in the electron density distribution function. Electron density measurements showed negligible difference between the average electron densities of pure SiCl4 and 60% N-2 in SiCl4 plasmas except at high power. Mass spectrometric results showed an increase in SiCl4 dissociation and a subsequent increase in Cl-2 production with the addition of nitrogen, accounting for the increase in etch rate. The enhanced dissociation is believed to be due in part to an increase in the average electron temperature. (c) 2005 The Electrochemical Society. [DOI: 10. 11-49/1.1860513] All rights reserved.